Arctic climate change: the past 100 years

The Arctic is a region particularly sensitive to climate change, since temperatures are, on average, near the freezing point of water. Slight shifts in the average temperature can greatly change the amount of ice and snow cover in the region, due to feedback processes. For example, as sea ice melts in response to rising temperatures, more of the dark ocean is exposed, allowing it to absorb more of the sun's energy. This further increases air temperatures, ocean temperatures, and ice melt in a process know as the "ice-albedo feedback" (albedo means how much sunlight a surface reflects). The 20% loss in Arctic sea ice in summer since 1979 has given rise to concerns that this "ice-albedo feedback" has taken hold and will amplify until the Arctic Ocean is entirely ice-free later this century. Should we be concerned? Has the Arctic been this warm in the past and the sea ice survived? The answers are yes, and yes.

Figure 1. Annual average change in near surface air temperature from stations on land relative to the average for 1961-1990, for the region from 60 to 90° north. Image credit: The Arctic Climate Impacts Assessment (ACIA).

The past 100 yearsThe Arctic Climate Impact Assessment (ACIA), published in November 2004, was a uniquely detailed study of Arctic climate compiled by 300 scientists over three years. The study found that while temperatures in the Arctic have increased significantly since 1980 (Figure 1), there was also a period in the 1930s and 1940s when temperatures were almost as warm. If one defines the Arctic as lying poleward of 62.5° north latitude (Polyakov, 2003), the 1930s and 1940s show up being warmest period in the past 100 years. Looking at Figure 1, one cannot dismiss the possibility that temperatures in the Arctic oscillate in a 50-year period, and we are due for a cooling trend that will take temperatures below normal by 2030.

However, the period since 1980 was a time when the entire globe (except the bulk of Antarctica) warmed, and the 1930s and 1940s were not. Thus, the 1930s and 1940s warming in the Arctic is thought to be fundamentally different. Furthermore, the past 20 consecutive years have all been above normal in temperature, whereas during the 1930s and 1940s there were a few cooler than average years interspersed with the very warm years. A detailed breakdown by month and region of the 100-year history of Arctic temperatures was performed by Overland et al. (2004). They found no evidence of a 50-year cycle in Arctic temperatures, and concluded that the warming since 1980 was unique. However, they stopped short of blaming the recent warming on human-emitted greenhouse gases (anthropogenic forcing). The ACIA, though, concluded that humans were likely to blame for the recent Arctic warming, but not definitely:It is suggested strongly that whereas the earlier warming was natural internal climate-system variability, the recent surface air temperature changes are a response to anthropogenic forcing. There is still need for further study before it can be firmly concluded that the increase in Arctic temperatures over the past century and/or past few decades is due to anthropogenic forcing."

This is the first in a series of five blogs on climate change in the Arctic that will appear every Monday and Thursday over the next two weeks. Next blog: The skeptics attack the ACIA report--and how the position of the pole star is indicative of Arctic climate change.

Also, be sure to visit our new Climate Change blog, written by Dr. Ricky Rood of the University of Michigan.

Weatherboychris no tropical developemnt is expected but if a weak low were to try to form it will only add to the rain amounts across south florida in the coming hours as this entire areas drifts north.

Part of the NWS discussion form earlier this morning...

THIS IS WHERE YOU GO ON A LIMB DUE TO THAT DATA HOLE THAT IS THEGULF OF MEXICO. THERE COULD BE...ARGUABLY A WEAK SFC LOW TRYING TODEVELOP SOMEWHERE AROUND THE YUCATAN PENINSULA BUT IT IS HARD TOFIND EVEN VIA HAND ANALYSIS. THIS IS PERHAPS WHAT GFS IS LATCHING ONTO WHICH IT DEVELOPS RATHER AGGRESSIVELY AS THE DAY PROGRESSES INRESPONSE TO UPR LVL S/W FORCING. IF THIS HAPPENS, THEN THERE IS NODOUBT SFC TROUGH TO OUR SOUTH SHOULD LIFT NORTH AS THE LOW AND UPRLVL S/W APPROACHES WEST CENTRAL AND SW FLORIDA TONIGHT INCREASINGSEVERE WEATHER THREAT ACROSS THE AREA.

Weak surface low isn't out of the question, for the gulf (though it looked more likely lastnight). Check the clouds down there on the RGB They're mostly in the lower levels. So shear wouldn't play as big apart unless it tried to strengthin, make higher clouds.

Ive recieved a couple of phone calls from some friends down in the keys and they have said its been pouring really hard for hours down there with gusty winds also in the mix.Hopefully things will begin to slow down as the afternoon approaches.

Hey everybody, Very active morning here across SOUTH FLORIDA. KEY WEST RADAR REALLY SHOWING HEAVY THUNDERSTORMS WITH ROTATION MOVING NORTH!I HAVE A FEELING WE MIGHT HAVE A LITTLE SEVERE WEATHER HERE IN MIAMI LATER ON THIS AFTERNOON!

V26R, we dont expect any rain in the Caribbean until June. Thats when the itcz gets to me, anyway. Further north, at Puerto Rico, Antigua etc. they have to wait on the first trop. wave off Africa to give them any real relief.

Yet more info on anthropogenic forcing. I agree it is a contribution to climate change but what is important is can we DO anything about it. What I am reading is that even if we stop or level gg production the climate will continue to change. The next critical question is how do we COPE with the changes and figure out what they are. Should we start farms in Greenland so we don't starve or what? Roll white permeable plastic membrane over the arctic or just start farming salmon there? We need bright people like the Dr. here to work on those questions too. It seems important to stop making climate change worse with greenhouse gas production but it is even more important not to make it worse by trying to "FIX" it without proper forethought.

Dr Masters, thanks for the info as always. I appreciate the cautious tone, and I appreciate your avoiding any sweeping statements, while still building a case that even the skeptics can't dismiss.This reminds me of the cigarette controversy a few decades ago. The tobacco industry always denied a link between smoking and cancer and heart disease etc, and insisted there was never a causal link, that it was always coincidence, in spite of all the studies that showed otherwise. Meanwhile millions were sickened and died over the years while the debate went on. This looks like the same deal, except by the time everyone reaches a consensus this time, Florida will be gone! ;-)